138 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



Family PALASTERINID.E Gregory (emend.). 



Palxasterinidx Gregory (part), Geol. Mag., dec. 4, vol. 6, 1899, p. 348 (contains 

 Palasterina, Schxnaster, and Schuchertia); Treat. Zool., vol. 3, Echinoderma, 

 1900, p. 250. 



Lindstromasterinse Gregory (part), Geol. Mag., dec. 4, vol. 6, 1899, p. 346 (contains 

 Lindstromaster and Uranaster). 



Palseasterinidse Sturtz, PalseontograpHca, vol. 36, 1890, p. 246. 



Progressive Phanerozonia developing large interbrachial arcs. 

 Ambulacral plates more or less alternate. Madreporite abactinal. 

 Disk large, pentagonal, and the rays separated by well-developed 

 interbrachial arcs. The inframarginal plates bound the animal and 

 are separated from the adambulacrals more or less completely by a 

 varying number of interbrachial plates. 



Abactinal surface with longitudinal columns of radial, supra- 

 marginal and accessory columns of plates, or the radial columns 

 may be reduced or even replaced by transverse rows of small accessory 

 pieces. The central region of the disk may retain a ring of larger 

 basal radial and supramarginal pieces. 

 Contains : 



Petraster Billings. 



Lindstromaster Gregory. 



Palasterina McCoy. 



Uranaster Gregory. 



Palxostella Sturtz. 



Pseudopalasterina Sturtz. 



Genus PETRASTER Billings. 



Plates 23, 26, 27. 



Petraster Billings, Geol. Surv. Canada, Can. Org. Rem., dec. 3, 1858, p. 79.— 

 Hall, Twentieth Rep. N. Y. State Cab. Nat. Hist., 1868, pp. 283, 294; rev. 

 ed., 1868=1870, pp. 325, 337. 



Palxaster (part) Zittel, Handb. Pal., vol. 1, 1879, p. 452. 



Palseasterina of some Authors. 



Generic characters. — Disk and interbrachial arches more or less 

 large. General shape pentagonal. Rays five, short and slender or 

 stout and tapering rapidly. 



Abactinal area of rays distally with one medial radial, two supra- 

 marginal and two inframarginal columns of plates. Between the 

 radial and supramarginal columns proximally are mserted columns 

 of accessory plates. In P. speciosus there arc five on each side of 

 the radial column. Between the supramarginal and inframarginal 

 columns in the axillary and basal ray regions are inserted columns 

 of ambital plates. In P. speciosus there are three. The plates 

 are more or less stellate, with numerous subcu-cular openings in the 

 angles between adjoining plates. 



